1. Field of the Invention
The present invention relates to the technical field of satellite television transmission and, more particularly, to a blind scan system and method in a Digital Video Broadcasting-Satellite (DVB-S) system.
2. Description of Related Art
In developing digital televisions, one of essential tasks is to establish a digital platform. In addition to pure hardware equipments such as a set-top box or television set, the digital platform needs to include digital channels and contents.
Current specifications for global digital televisions are grouped essentially into several types according to market segments: Advanced Television Systems Committee (ATSC) systems for American-based markets, Digital Video Broadcasting (DVB) systems for Euro-based markets, Digital Terrestrial Multimedia Broadcasting (DTMB) systems for China-based markets, and ISDB-T systems for Japan-based markets. The DVB systems can be further divided into DVB-C (Cable) providing the wired television standards, DVB-S (Satellite) providing the satellite television standards, and DVB-T (Terrestrial) providing the terrestrial wireless television standards.
An official system provider can transmit a DVB-S signal to a satellite antenna disposed on a building through a satellite located over 32000 km and above. In this case, a quadrature phase shift keying (QPSK) is applied to transmit MPEG2 data, and a multi-channel carrier frequency and symbol rate can be pre-stored in a receiver in order to rapidly receive the programs.
However, when the carrier frequency and symbol rate are changed for an updated channel, such a way is unable to receive the programs on the updated channel smoothly. Accordingly, for such a DVB-S receiver, a blind scan function is required in order to provide a simple operating mode to thereby allow a user to have an automatic program scan without knowing the detailed parameters of programs received by a satellite in advance. Scan speed and accuracy of parameter estimation are the most important factors in evaluating the performance of a blind scan procedure. Rapid scan reduces waiting time of a user in the procedure.
FIG. 1 is a block diagram of a typical receiver. As shown in FIG. 1, the operation principle is first to use the controller 11 for tuning the analog tuner 12 to a carrier frequency (CF). Next, the filter bank (not shown) and the timing recovery loop (not shown) in the baseband demodulation chip 13 are started to operate with the least symbol rate. The symbol rate is increased when the loop cannot converge. When the symbol rate is over a preset maximum and the loop cannot converge, it indicates that there is no signal at this frequency, and in this case the carrier frequency of the analog tuner is updated by adding a step to the original basis. Accordingly, the above process is repeated until the loop converges and the signal and associated parameters are detected.
Such a process has the disadvantage of very slow scan speed. Since the possible symbol rate used by a DVB-S system may be varied in a very wide range, such as from 1M to 45M bauds, and a satellite signal occupies a quite wide spectrum, such as an input range from 950 MHz to 2150 MHz for a Ku band tuner, so that the combination produces numerous possibilities. Accordingly, it requires long time to complete the entire possibility scan once through the blind scan procedure. In addition, it takes much time to change the carrier frequency of the analog tuner 12, which significantly prolongs the scan time due to the frequent step carrier frequencies. Further, the step resolution of the analog tuner is limited to, typically hundreds of KHz. Thus, only changing the frequency of the analog tuner cannot accurately detect the carrier frequency. Moreover, the convergence of the loop is very slow, so that loop-scanning the symbol rate is quite slow. Therefore, the typical frequency scan has a very slow scan speed.
Accordingly, it is desirable to provide an improved blind scan system and method to mitigate and/or obviate the aforementioned problems.